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Thread: 7-zip 4.54 beta is out!

  1. #1
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    Quote Originally Posted by encode
    Whats new:
    - Decompression speed was increased for LZMA, Deflate, RAR and CAB.
    - Some minor changes in GUI
    www.7-zip.org

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    Programmer giorgiotani's Avatar
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    I'm testing it, it seems good and the speed improvement is noticeable, Igor Pavlov really did a good work to sqeeze out further speed for decompression!
    I think the (soon) upcoming PeaZip 1.9.1 will have frontend for it rather than for 4.53, on Windows version.

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    Well, 7-zip 4.55 is already out.
    Igor is working fast !!!

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    Programmer giorgiotani's Avatar
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    Probably it's primarily a fix-oriented release, possibly due to issue posted in http://sourceforge.net/forum/forum.php?thread_id=1 816837&forum_id=45797
    However this and the previous one perform very well!

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    The Founder encode's Avatar
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    Finally Igor changed:

    cxt = (cxt << 1) + y;

    to

    cxt = (cxt + cxt) + y; // (cxt = (cxt + cxt) + 1)

    However, even better use:

    cxt += (cxt + y);


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    these lines affects what .. performance..?

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    The Founder encode's Avatar
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    Quote Originally Posted by maadjordan
    these lines affects what .. performance..?
    Yep. I briefly looked the 7-Zips source to find out why new release has a faster decompression. One of the changes Ive found - this trick that used for a long long time with PAQ coders (and with LZPM as well )


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    Matt Mahoney's Avatar
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    Just a quick test, but g++ optimizes cxt<<1 to cxt+cxt. (I believe a shift takes 2 clocks on a Pentium 4, add takes 1/2 clock).

    C: mp>type a.cpp
    extern "C" unsigned int f(unsigned int x, int y) {
    return (x<<1) + y;
    }

    C: mp>g++ -O -S -fomit-frame-pointer a.cpp

    C: mp>type a.s
    .file "a.cpp"
    .text
    .align 2
    .globl _f
    .def _f; .scl 2; .type 32; .endef
    _f:
    movl 4(%esp), %eax
    addl %eax, %eax
    addl 8(%esp), %eax
    ret

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    is there a way to time out each phase of program or group of lines to check the speed of data flow and check wither there is a heckup process that dealy such flow.. i know that the easiest way to compile each process as a seperate rogram and time it.. is there another way..

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    Intel Vtune, AMD CodeAnalyst

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